Effect of Al2O3 on the structure and microwave dielectric properties of Ca0.7Ti0.7La0.3Al0.3O3

The effect of excess Al2O3 on the densification, structure and microwave dielectric properties of Ca0.7Ti0.7La0.3Al0.3O3 (CTLA) was investigated. CTLA ceramics were prepared using the conventional mixed oxide route. Excess Al2O3 in the range of 0.1–0.5 wt% was added. It was found that Al2O3 improved the densification. A phase rich in Ca and Al was found in the microstructure of Al2O3 doped samples. Additions of Al2O3 coupled with the slow cooling after sintering improved the microwave dielectric properties. CTLA ceramics with 0.25 wt% Al2O3 cooled at 5 °C/h showed high density and a uniform grain structure with ɛr = 46, Q × f = 38,289 and τf = +12 ppm/°C at 4 GHz. XRD and TEM examinations showed the presence of (1 1 2) and (1 1 0) type twins arising from a−a−c+ tilt system with the presence of anti-phase domain boundaries from the displacement of A-site cations of the orthorhombic perovskite structure.